Vigilance states in children are important contributors to behavior, and excessive daytime sleepiness (EDS) may be a risk for poor behavioral adjustment. EDS may underlie or affect such problems as inattentiveness, hyperactivity, and impulsivity, but developmental differences in the manifestation of EDS may obscure this relationship. Younger children may respond to sleepiness with overactivity and disruptive behavior, while older children may respond with lethargy. This project systematically assesses children's sleep-related behaviors to determine the formal behavioral manifestations of their responses to physiological sleepiness and whether the responses change as a function of childhood development (including puberty). Two studies in normal children are proposed. Study 1 involves 5 groups of normal boys and girls [ages 6 to 8.5 years; 8.5 to 11 years; 11 to 13.5 years (2 subgroups: prepubertal and mid- to late pubertal), and 13.5 through 15 years] challenged with one night of acute sleep restriction to 40% of basal sleep time. Evaluations include actigraphic, behavioral observation, performance, physiological, and introspective measures. Variations in children's responses to acute sleep restriction are assessed as a function of age, sex, and pubertal status. Study 2 investigates prolonged and repeated sleep restriction. Children are exposed to either two consecutive weeks of sleep reduction (75% of baseline) or to two nonconsecutive weeks of sleep reduction. Laboratory measures of sleep, physiological sleepiness, performance, and behavioral observation, as well as classroom observations and teacher and parent assessments are used to evaluate the hypotheses that a week of moderate sleep restriction affects behavior; the response to moderate sleep restriction changes as a function of age; and prolonged sleep restriction differentially affects waking behavior in comparison to repeated sleep restriction. These studies provide the opportunity to characterize developmentally relevant changes in daytime sleepiness, and they give a comprehensive view of children's responses to the experimental interventions. The results may provide direction for understanding how brain states interact in the regulation of behavior at different ages. The project will also define the extent to which sleepiness is a risk for childhood behavior dysfunction. Such data may be useful with regard to the interpretation of clinical symptoms and perhaps for the classification of clinical syndromes. This project provides the first systematic assessment of the important behavioral dimension of sleepiness in children, giving an opportunity to understand in much greater depth not only the developmental manifestations of sleepiness but also certain fundamental aspects of sleep/wake regulation in children and adolescents.